1. Field of the Invention
The present invention relates to a support arm. Especially, the present invention relates to a support arm, which is capable of automatically self-locking. The support arm not only has a function of being locked for positioning, but also has a benefit of supporting a heavier load.
2. Description of the Related Art
As the era and age of information technology comes, more and more processes or works must be done through the use of computer equipment, either in work or in live. However, computer equipments such as a mouse, a printer, a scanner, a display monitor, or a keyboard, takes a lot of space on the desk or table. Especially, when the desk is small, it is inconvenient to use or operate for a user. Notwithstanding the foregoing, when the computer equipments are installed, their height and angle are not suit for users of different sizes. As a result, injuries suffered on the job are open caused by using computer equipments, such as carpal tunnel syndrome and repetitive strain injury affected arms, hands eyes, muscles, and even bones. The computer equipments are often placed on support arms having flexible structure for reducing the injuries.
A common used support arm is shown in FIG. 1. The conventional support arm consists of a chassis 10, a front arm 17, a hang arm 20, a connecting rod 25, and a spring 27. The chassis 10 is a base frame having a shape like “U”. The front arm 17 is a frame having a shape like reversed “U”. The front arm 17 is provided at its top with a swing joint 171 and a connecting plate 173. The hang arm 20 is a connecting rod having a cross-section like reversed “U”. The both lower ends of the side walls of the reversed “U” of the hang arm 20 are provided with a first axel bolt 11 so as to be assembled to the chassis 10. The lower end of hang arm 20 forms a rotatable joint with the chassis 10 by the first axel bolt 11. The both upper ends of the side walls of the reversed “U” of the hang arm 20 are provided with a second axel bolt 12. The second axel bolt 12 is assembled with the front arm 17. The upper end of the hang arm 20 forms a rotatable joint with the front arm 17 by the second axel bolt 12. The both upper ends of the hang arm 20 are respectively provided with arc slots 21. A third axel bolt 13 is disposed through the arc slots 21 onto the side walls of the front arm 17, so as to fix the hang arm 20 to the front arm 17. Connecting rod 25 is a rod having a cross section like “U”. The lower ends of both side walls of the connecting rod 25 are respectively provided with axel holes 251. A fourth axel bolt 14 is disposed through the axel holes 251 onto the chassis 10, to fix the connecting rod 25 to the chassis 10. Therefore, the lower end of the connecting rod 25 forms a rotatable joint with the chassis 10 by the fourth axel bolt 14. The both lower ends of the side walls of the connecting rod 25 are respectively provided with arc slots 253. The first axel bolt 11 is disposed through the arc slots 253. A third axel bolt 13 is disposed through the both upper ends of side walls of the connecting rod 25 onto the front arm 17, so that the both upper ends of the side walls of the connecting rod 25 form a rotatable joint with the front arm 17. The spring 27 is a coil type spring sleeved on the first axel bolt 11. One end of the spring 27 is disposed against the connecting rod 25, and the other end of the spring 27 is disposed against the fourth axel bolt 14, so as to provide an appropriate upward reaction force.
Please refer to FIGS. 2A, 2B, 3A, and 3B at the same time. FIG. 2A is a cross-sectional view of the conventional support arm at a first rotating angle. FIG. 2B is an enlarged cross-sectional view of the conventional support arm at the first rotating angle. FIG. 3A is a cross-sectional view of the conventional support arm at a second rotating angle. FIG. 3B is an enlarged cross-sectional view of the conventional support arm at the second rotating angle. As shown in the figures, a stop bolt 15 is disposed near the rear edges of the both side walls of the chassis 10. Arc edges 255, whose center is axel hole 251, are formed at the rear edges of the lower ends of both side walls of the connecting rod 25. The diameter of the axel hole 251 is larger than the diameter of a fourth axel bolt 14 disposed therein. The position of the stop bolt 15 is higher than the position of the fourth axel bolt 14. Therefore, when the connecting rod 25 is not moving, it will droop due to the weight of a LCD display monitor (not shown). The distance from the axel hole 251 to the arc edge 255 is larger the distance from the center of the fourth axel bolt 14 to the arc edge 255. The arc edges 255, formed at the rear edges of the lower ends of both side walls of the connecting rod 25, will engage with the stop bolt 15, to form a support force acting on the hang arm 20, in order to support the LCD display monitor (not shown) on the connecting plate 173 which is mounted on the front arm 17. Furthermore, the diameter of the axel hole 251 is larger than the diameter of the fourth axel bolt 14 disposed the axel hole 251, that is, there is a space formed between the axel bolt 251 and the fourth axel bolt 14. When the connecting rod 25 is lifted up slightly, the arc edges 255, formed at the rear edges of the lower ends of both side walls of the connecting rod 25, will disengage from the stop bolt 15. Then, the hang arm 20 and the connecting rod 25 can be moved smoothly, so as to adjust the position of the LCD display monitor.
The conventional display monitor support arm has the benefit of simple components. However, when operating and manufacturing, it still has deficiencies as stated below:
1. When support arm of the display monitor is adjusted to a required angle, it is positioned by the engagement of the stop bolt and the arc edges of the connecting rod to generate a friction force. After long time of use, the components will be worn which results in difficulty of positioning.
2. The supporting force for positioning comes from the engagement between the stop bolt and the arc edges, therefore its loading capacity will be limited.
3. The size and position of the axel hole of the connecting rod, the arc edges, and the fourth axel bolt must be precisely designed, manufactured, and assembled, in order to form the engagement. Therefore, it takes a lot of cost of manufacturing.